Then there is no point in calling it Episode VII. Just go the Marvel route and call it Star Wars: Whatever.

It is being called Episode VII. That is EPISODE VII of one continuing story...

The reason would simply be for branding and marketing reasons. Regardless of its content (i.e. whether it's a direct continuation of ROTJ or a new beginning following its events with new characters) the next Star Wars movie would likely do better if sold as the 7th movie than as a new one.

A more extreme example of this practice are Daniel Craig's James Bond movies. Despite rebooting the story back to the beginning with zero narrative ties to any of its predecessors, Casino Royale is more often marketed and described as the 21st James Bond movie, as opposed to the first of a new series or a remake of the old Casino Royale.

P.S.: What Marvel-produced movie did the 'Star Wars: Whatever' approach as you described when not directly continuing a movie franchise yet still having it based in the same continuity?